This invention relates to an improvement in the prior art type of inspiratory force adapter as shown in FIG. 1. Such an adapter consists of a molded plastic hollow body 10 having one tubular end 12 adapted to be connected onto the outer end of a tracheostomy tube 14, the other end of the tracheostomy tube being connected to the patient. The tubular member 12 extends to a ridge 16 which lies in a plane substantially perpendicular to the longitudinal axis of member 12. Beyond the ridge 16, body 10 has a tapered hollow section 18 which tapers down to a tubular output member 20 adapted to be connected to a flexible tube 22 which is connected to the usual inspiratory pressure gauge.
The upper face 24 of section 18 is disposed at an angle of about 45.degree. with respect to the longitudinal axis of member 12 and is provided with a finger port 26 consisting of an opening into the hollow interior of body 10.
When in use, the tubular member 12 is grasped between the thumb 28 and second finger 30 of the operator. The sides of these two fingers rest against the ridge 16 which thus may be termed a "finger ridge". When it is desired to measure the inspiratory force exerted by the patient's diaphragm, the index finger 32 of the operator is pressed against the port 26 just before the patient begins the inhalation part of his breathing cycle. Thus, index finger 32 closes port 26 and the inhalation by the patient reduces the pressure within the system in which the adapter is located. Such reduction in pressure is measured by the pressure gauge connected to the tube 22 in accordance with the well known procedure for such a measurement.
A problem of such prior art device arises from the fact that any transverse motion imparted to the end of tracheostomy tube 14 is transmitted to the point at which the tracheostomy tube enters the incision in the patient's throat. Such motion is disturbing to the patient and otherwise highly undesirable. When in use, such prior art device tends to produce such motion to an undescriable degree.
The present invention recognizes that this is due to several factors. In each human hand, the thumb 28 is normally about an inch wide and is appreciably wider than the width of the second finger 30. Such difference is about two tenths of an inch. Therefore, when the thumb and index finger abut the finger ridge 16, the center 34 of the pressure area of the thumb 28 is displaced by a distance d, of about one-tenth of an inch from the center 36 of the pressure area of the second finger 30. This displacement of the points of maximum pressure by the thumb and second finger produces a couple which tends to rotate the body 10 around the point 34.
This invention also recognizes that the direction, along which the index finger 32 exerts its pressure lies along the line 38. Line 38 is substantially perpendicular to face 24 and passes through the center of finger port 26. The line, along which thumb 28 exerts its pressure through point 34, is designated as 40. It will be noted that line 38 intersects line 40 at a point substantially below point 34. As a result the forces exerted by the thumb 28 and the index finger create an additional couple tending to rotate the body 10 in the same direction as the couple between the thumb 28 and the second finger 30. Consequently, it is very difficult for the operator to restrain a tilting motion of body 10 during the operation of the device. As indicated above such motion is highly undesirable.